What is War Weight in Clash of Clans?

War weight is a factor effecting clan war match making

Specific buildings have different weights

For example, x-bows and inferno towers have high weight so building them would increase the weight of your base, making your war mirrors base to be harder and more levelled

This link shows weight comparison an example of how it effects match making as the game attempt to find a war where all player have an even match https://www.clashtrack.com/images/weight_comparison.jpg

The higher you war weight, the higher level your opponent (mirror) in war would/should be

https://www.clashtrack.com/en/war-weight